Digital lighting technologies, i.e., illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g., red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects.
Recently, retrofit solid state light source devices, such as LED lamps, have entered the market in large numbers, including solid state light source devices that may be part of a dimmer circuit. For example, dimmable screw base LED lamps may be configured to screw into lamp sockets designed for screw base incandescent light bulbs, and pin base LED lamps may be configured to plug into pin sockets designed for pin base incandescent and/or fluorescent bulbs.
Dimmers are usually connected in series with the load (2-wire connection), and depend for their proper operation on the conduction of current through the load. In case of a conventional incandescent lamp, the load is behaving like a resistor, but in case of an electronic load (energy-saving LED lamp), the load characteristics differ considerably in amplitude and time (during a mains cycle). For simplicity, only (phase cut) dimmers are mentioned here, but the same holds for electronic switches with or without advanced controls (light sensors, presence detectors, timer circuits, remote controls, etc.)
Retrofit LED lamps are often incompatible with existing dimmers, which results in flickering and/or flashing of the LED lamps, or no light output at all. Flickering may occur at particular dimming phase angles, or over a wide range of dimming phase angles, depending on the LED lamp/dimmer combination, as well as the number of LED lamps on the dimmer circuit. For example, some dimmers function correctly for small numbers of LED lamps per dimmer circuit, but begin to cause flicker as the number of LED lamps increases. Also, for dimmers that require continuous small current flow through the LED lamps to power the dimmer circuitry (even when the lamps are off), performance is especially inadequate. Notably, flickering may be reduced by including at least one incandescent lamp among the LED lamps in the dimmer circuit. However, inclusion of an incandescent lamp compromises the high efficiency and long lifetimes of the LED lamps, and availability of incandescent lamps may be limited in the future. Also, inclusion of an incandescent lamp is not an option when the dimmer circuit consists of a single lamp.
Thus, there is a need in the art for a circuit that can be added to a retrofit solid state light source in a dimmer circuit, which reduces or eliminates flicker and/or otherwise improves compatibility between the low-power light source and a control circuit therefor, for example, between the light source and the dimmer circuit, regardless of the type of dimmer, the dimming phase angle and/or the number of solid state light sources included in the dimmer circuit.